Dissertations / Theses: 'Semiconductor Properties of ZnO'

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Lee, William (Chun-To). "Harvesting Philosopher's Wool: A Study in the Growth, Structure and Optoelectrical Behaviour of Epitaxial ZnO." Thesis, University of Canterbury. Electrical and Computer Engineering, 2008. http://hdl.handle.net/10092/2507.

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This thesis is about the growth of ZnO thin films for optoelectronic applications. ZnO thin films were grown using plasma assisted molecular beam epitaxy and were studied using various conventional and novel characterisation techniques. The significance of different growth variables on growth efficiency was investigated. The growth rate of ZnO films was found to be linearly dependent on the Zn flux under O-rich growth conditions. Under Zn-rich conditions, the growth rate was dependent on both atomic and molecular oxygen flux. By characterising the oxygen plasma generated using different RF power and aperture plate designs and correlating the results with the growth rates observed, it was found that atomic oxygen was the dominant growth species under all conditions. Molecular oxygen also participated in the growth process, with its importance dependent on the aperture plate design. In addition, an increase in growth temperature was found to monotonically decrease the growth rate. A growth rate of 1.4 Å/s was achieved at a growth temperature of 650 ℃ by using an oxygen flow rate of 1.6 standard cubic centimetres utilising a plasma source with a 276 hole plate operating at 400 W, and a Zn flux 1.4✕10¹⁵ atoms/cm²⋅s. Characterisation of the MBE grown thin films revealed that the qualities of ZnO thin films were dependent on the growth conditions. Experimental evidence suggested that a maximum adatom diffusion rate can be achieved under Zn-rich conditions, giving samples with the best structural quality. O-rich conditions in general led to statistical roughening which resulted in rough and irregular film surfaces. Experimental results also suggested that by increasing the atomic oxygen content and decreasing the ion content of the plasma, the excitonic emission of the ZnO thin films can possibly be improved. It was also found that the conductivity of the films can possibly be reduced by increasing the plasma ion content. By investigating the evolution of the buffer layer surface during the early stages of growth, dislocation nucleation and surface roughening were found to be important strain relief mechanisms in MBE grown ZnO thin films that affected the crystal quality. The usage of LT-buffer layers was found to improve substrate wetting, and was shown to significantly reduce dislocation propagation. Further strain reduction was achieved via the application of a 1 nm MgO buffer layer, and a significant reduction of carrier concentration and improvement in optical quality was subsequently observed. A carrier concentration of <1✕10¹⁶ cm⁻³ and a near band emission full width half maximum of 2 meV was observed for the best sample. The study of electrical characteristics using the variable magnetic field Hall effect confirmed the existence of a degenerate carrier and a bulk carrier in most MBE grown ZnO thin films. The bulk carrier mobility was measured to be ~120 - 150 cm²/Vs for most as-grown samples, comparable to the best reported value. A typical bulk carrier concentration of ~1✕10¹⁶ - 1✕10¹⁸ cm⁻³ was observed for as-grown samples. Annealing was found to increase the mobility of the bulk carrier to ~120 - 225 cm²/Vs and decrease the bulk carrier concentration by two orders of magnitude. Using time resolved photoluminescence, it was found that the radiative recombination in MBE grown ZnO thin films was dominated by excitonic processes, and followed a T³⁄² trend with temperature. A maximum radiative lifetime of 10 ns was observed for as-grown samples. The non-radiative lifetime in ZnO thin films was dominated by the Shockley-Read-Hall recombination processes. The modelling of the temperature dependence of the non-radiative lifetime suggested that an electron trap at ~0.065 eV and a hole trap at ~0.1 eV may be present in these samples. The application of time resolved photoluminescence also allowed the direct observation of carrier freeze-out in these ZnO films at low temperature.

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Yang, Li Li. "Synthesis and Characterization of ZnO Nanostructures." Doctoral thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-60815.

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One-dimensional ZnO nanostructures have great potential applications in the fields of optoelectronic and sensor devices. Therefore, it is very important to realize the controllable growth of one-dimensional ZnO nanostructures and investigate their properties. The main points for this thesis are not only to successfully realize the controllable growth of ZnO nanorods (ZNRs), ZnO nanotubes (ZNTs) and ZnMgO/ZnO heterostructures, but also investigate the structure and optical properties in detail by means of scanning electron microscope (SEM), transmission electron microscope (TEM), resonant Raman spectroscopy (RRS), photoluminescence (PL), time resolved PL (TRPL), X-ray photoelectron spectroscopy (XPS) and Secondary ion mass spectrometry (SIMS). For ZNRs, on one hand, ZNRs have been successfully synthesized by a two-step chemical bath deposition method on Si substrates. The diameter of ZNRs can be well controlled from 150 nm to 40 nm through adjusting the diameter and density of the ZnO nanoparticles pretreated on the Si substrates. The experimental results indicated that both diameter and density of ZnO nanoparticles on the substrates determined the diameter of ZNRs. But when the density is higher than the critical value of 2.3×108cm-2, the density will become the dominant factor to determine the diameter of ZNRs. One the other hand, the surface recombination of ZNRs has been investigated in detail. Raman, RRS and PL results help us reveal that the surface defects play a significant role in the as-grown sample. It is the first time to the best of our knowledge that the Raman measurements can be used to monitor the change of surface defects and deep level defects in the CBD grown ZNRs. Then we utilized TRPL technique, for the first time, to investigate the CBD grown ZNRs with different diameters. The results show that the decay time of the excitons in ZNRs strongly depends on the diameter. The altered decay time is mainly due to the surface recombination process. A thermal treatment under 500°C can strongly suppress the surface recombination channel. A simple carrier and exciton diffusion equation is also used to determine the surface recombination velocity, which results in a value between 1.5 and 4.5 nm/ps. Subsequently, we utilized XPS technique to investigate the surface composition of as-grown and annealed ZNRs so that we can identify the surface recombination centers. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Finally, on the basis of results above, we explored an effective way, i.e. sealing the beaker during the growth process, to effectively suppress the surface recombination of ZNRs and the suppression effect is even better than a 500oC post-thermal treatment. For ZNTs, the structural and optical properties have been studied in detail. ZNTs have been successfully evolved from ZNRs by a simple chemical etching process. Both temperature-dependent PL and TRPL results not only further testify the coexistence of spatially indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their strong enhancement of luminescence intensity. For ZnMgO/ZnO heterostructures, the Zn0.94Mg0.06O/ZnO heterostructures have been deposited on 2 inch sapphire wafer by metal organic chemical vapor deposition (MOCVD) equipment. PL mapping demonstrates that Mg distribution in the entire wafer is quite uniform with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors in Zn0.94Mg0.06O/ZnO heterostructures have been investigated by SIMS in detail. All the SIMS depth profiles of Mg element have been fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC is two orders of magnitude lower than that of annealing samples, which clearly testifies that the deposited temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells. This thesis not only provides the effective way to fabricate ZNRs, ZNTs and ZnMgO/ZnO heterostructures, but also obtains some beneficial results in aspects of their optical properties, which builds theoretical and experimental foundation for much better understanding fundamental physics and broader applications of low-dimensional ZnO and related structures.
Endimensionella nanostrukturer av ZnO har stora potentiella tillämpningar för optoelektroniska komponenter och sensorer. Huvudresultaten för denna avhandling är inte bara att vi framgångsrikt har realiserat med en kontrollerbar metod ZnO nanotrådar (ZNRs), ZnO nanotuber (ZNTs) och ZnMgO/ZnO heterostrukturer, utan vi har också undersökt deras struktur och optiska egenskaper i detalj. För ZNRs har diametern blivit välkontrollerad från 150 nm ner till 40 nm. Den storlekskontrollerande mekanismen är i huvudsak relaterad till tätheten av ZnO partiklarna som är fördeponerade på substratet. De optiska mätningarna ger upplysning om att ytrekombinationsprocessen spelar en betydande roll för tillväxten av ZNR. En värmebehandling i efterhand vid 500 grader Celsius eller användande av en förseglad glasbägare under tillväxtprocessen kan starkt hålla nere kanalerna för ytrekombinationen.För ZNT, dokumenterar vi inte bara samexistensen av rumsliga indirekta och direkta övergångar på grund av bandböjning, men vi konstaterar också att vi har mindre icke-strålande bidrag till den optiska emissionsprocessen i ZNT. För ZnMgO/ZnO heterostrukturer konstaterar vi med hjälp av analys av Mg diffusionen i den växta och den i efterhand uppvärmda Zn(0.94)Mg(0.06)O filmen, att en tillväxt vid 700 grader Celsius är den mest lämpliga för att växa ZnMgO/ZnO heterostrukturer eller kvantbrunnar. Denna avhandling ger en teoretisk och experimentell grund för bättre förståelse av grundläggande fysik och för tillämpningar av lågdimensionella strukturer.
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Li, Yun. "First Principle Calculations of the Structure and Electronic Properties of Pentacene Based Organic and ZnO Based Inorganic Semiconducting Materials." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc115112/.

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In this thesis, I utilize first principles density functional theory (DFT) based calculations to investigate the structure and electronic properties including charge transfer behaviors and work function of two types of materials: pentacene based organic semiconductors and ZnO transparent conducting oxides, with an aim to search for high mobility n-type organic semiconductors and fine tuning work functions of ZnO through surface modifications. Based on DFT calculations of numerous structure combinations, I proposed a pentacene and perfluoro-pentacene alternating hybrid structures as a new type of n-type semiconductor. Based on the DFT calculations and Marcus charge transfer theory analysis, the new structure has high charge mobility and can be a promising new n-type organic semiconductor material. DFT calculations have been used to systematically investigate the effect of surface organic absorbate and surface defects on the work function of ZnO. It was found that increasing surface coverage of organic groups and decreasing surface defects lead to decrease of work functions, in excellent agreement with experimental results. First principles based calculations thus can greatly contribute to the investigating and designing of new electronic materials.

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Schwarz, Casey Minna. "Radiation Effects on Wide Band Gap Semiconductor Transport Properties." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5488.

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In this research, the transport properties of ZnO were studied through the use of electron and neutron beam irradiation. Acceptor states are known to form deep in the bandgap of doped ZnO material. By subjecting doped ZnO materials to electron and neutron beams we are able to probe, identify and modify transport characteristics relating to these deep accepter states. The impact of irradiation and temperature on minority carrier diffusion length and lifetime were monitored through the use of the Electron Beam Induced Current (EBIC) method and Cathodoluminescence (CL) spectroscopy. The minority carrier diffusion length, L, was shown to increase as it was subjected to increasing temperature as well as continuous electron irradiation. The near-band-edge (NBE) intensity in CL measurements was found to decay as a function of temperature and electron irradiation due to an increase in carrier lifetime. Electron injection through application of a forward bias also resulted in a similar increase of minority carrier diffusion length. Thermal and electron irradiation dependences were used to determine activation energies for the irradiation induced effects. This helps to further our understanding of the electron injection mechanism as well as to identify possible defects responsible for the observed effects. Thermal activation energies likely represent carrier delocalization energy and are related to the increase of diffusion length due to the reduction in recombination efficiency. The effect of electron irradiation on the minority carrier diffusion length and lifetime can be attributed to the trapping of non-equilibrium electrons on neutral acceptor levels. The effect of neutron irradiation on CL intensity can be attributed to an increase in shallow donor concentration. Thermal activation energies resulting from an increase in L or decay of CL intensity monitored through EBIC and CL measurements for p-type Sb doped ZnO were found to be the range of Ea = 112 to 145 meV. P-type Sb doped ZnO nanowires under the influence of temperature and electron injection either through continuous beam impacting or through forward bias, displayed an increase in L and corresponding decay of CL intensity when observed by EBIC or CL measurements. These measurements led to activation energies for the effect ranging from Ea = 217 to 233 meV. These values indicate the possible involvement of a SbZn-2VZn acceptor complex. For N-type unintentionally doped ZnO, CL measurements under the influence of temperature and electron irradiation by continuous beam impacting led to a decrease in CL intensity which resulted in an electron irradiation activation energy of approximately Ea = 259 meV. This value came close to the defect energy level of the zinc interstitial. CL measurements of neutron irradiated ZnO nanostructures revealed that intensity is redistributed in favor of the NBE transition indicating an increase of shallow donor concentration. With annealing contributing to the improvement of crystallinity, a decrease can be seen in the CL intensity due to the increase in majority carrier lifetime. Low energy emission seen from CL spectra can be due to oxygen vacancies and as an indicator of radiation defects.
ID: 031001520; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Advisers: Elena Flitsiyan, Leonid Chernyak.; Title from PDF title page (viewed August 19, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 104-109).
Ph.D.
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Physics
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Mahmood, Farkhund Shakeel. "Electrical and optical properties of RF sputtered ZnO thin films." Thesis, Keele University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297202.

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Koch, Sandro. "Electrical and optical properties of hydrogen-related complexes and their interplay in ZnO." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-187905.

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The commercial breakthrough of ZnO-based devices is hampered mainly by the unipolar n-type conductivity of this material. Hydrogen, which is known to form both electrically active and inactive complexes in ZnO, is considered as a main cause of this behavior. However, the existing literature is incomplete and partly contradictory. The object of the present thesis is a comprehensive investigation of the properties of two hydrogen-induced shallow donors HBC and HO, the hydrogen molecule H2, and a hydrogen-related defect, which gives rise to local vibrational modes (LVMs) at 3303 and 3320 cm-1, in ZnO and their interaction. The defects are characterized by Raman spectroscopy, infrared absorption spectroscopy, photoconductivtity (PC) and photoluminescence measurements. Based on the PC technique, a novel and highly sensitive spectroscopic approach is established, which is applicable for probing LVMs in strongly absorbing spectral regions. This technique enables the detection of the local modes of HO at 742 and 792 cm-1 in the neutral charge state. In consequence, earlier theoretical predictions regarding the microscopic structure of this shallow donor can be verified. In Raman measurements the electronic 1s→2s transition of HO is identified at 273 cm-1. This quantity is found to blue-shift with the HO defect concentration. A similar blue-shift of the 1s→2s(2p) donor transition of HBC is assigned to local lattice strain which was generated during high temperature processes. A Raman study of the H2 molecule covers its formation, stability, lattice position and interplay with the ZnO host. In particular, the role of H2 for the continuous generation of HO and HBC and the related n-type behavior is elaborated. The analysis unambiguously confirms that the so-called “hidden hydrogen” species is indeed H2. Moreover, the observation of the ortho-para-conversion process and the coupling to the host phonons contribute to a general understanding of H2 in semiconductors. Experimental results of the LVMs of 3303 and 3320 cm-1 in conjunction with model calculations yield an underlying defect containing three hydrogen atoms. This complex Y–H3 exhibits two configurations, which differ only in the orientation of one chemical bond. The findings are consistent equally with a zinc vacancy decorated with three hydrogen atoms and an ammonia molecule, respectively. Earlier models proposed in the literature are discarded. Measurements of concentration profiles by using Raman spectroscopy reveal the local distribution of the hydrogen-related defects as well as lattice imperfections. At the surface, where oxygen vacancies are present, HO is identified as the dominant shallow donor. Below, in parts of the crystal with low damage, HBC is the prevalent defect. In the sample center, characterized by a significant amount of zinc vacancies, the concentrations of H2 and Y–H3 show their maxima. By recording concentration profiles after thermal treatments a spatially resolved investigation of the interplay of these hydrogen-related defects is possible
Der kommerzielle Durchbruch von ZnO-basierten Bauelementen ist hauptsächlich durch die beständige n-Typ Leitung des Materials eingeschränkt. Wasserstoff, der sowohl elektrisch aktive als auch inaktive Komplexe in ZnO formt, gilt als ein Hauptverursacher dieses Verhaltens. Jedoch ist die bestehende Literatur zu derartigen Defekten unvollständig, teils auch widersprüchlich. Gegenstand der vorliegenden Arbeit sind umfassende Untersuchungen der beiden wasserstoffinduzierten Donatoren HBC und HO, des Wasserstoffmoleküls H2 und eines Wasserstoffdefekts mit lokalen Schwingungsmoden (LSMn) bei 3303 und 3320 cm-1 in ZnO hinsichtlich ihrer Eigenschaften und gegenseitigen Wechselwirkung. Die Charakterisierung der Komplexe erfolgt mit Hilfe von Raman-Spektroskopie, Infrarot-Absorptionsspektroskopie, Photoleitfähigkeits- (PC) und Photolumineszenzmessungen. Basierend auf der PC Technik wird eine neuartige, hochsensitive Spektroskopiemethode etabliert, welche auch in stark absorbierenden Spektralbereichen anwendbar ist. Diese Technik ermöglicht erstmals die Detektion der LSMn von HO bei 742 und 792 cm-1 im neutralen Ladungszustand. Das experimentelle Ergebnis verifiziert theoretische Vorhersagen zur mikroskopischen Struktur dieses flachen Donators. In Raman-Messungen wird der elektrische 1s→2s Übergang von HO bei 273 cm-1 identifiziert und eine Blauverschiebung dieser Größe mit zunehmender HO-Konzentration beobachtet. Der Donator HBC zeigt ebenfalls eine Blauverschiebung des elektrischen 1s→2s(2p) Übergangs, welche durch lokale Gitterverzerrungen nach Hochtemperaturbehandlungen bedingt ist. Eine Raman-Studie charakterisiert das H2-Molekül in Bezug auf seine Bildung, Stabilität, Gitterposition und die Wechselwirkung mit dem ZnO-Kristall. Insbesondere wird seine Rolle für die fortwährende Bildung der Donatoren HO und HBC und des damit verbundenen n-Typ Verhaltens herausgearbeitet. Die Analyse ergibt die eindeutige Identifizierung der in der Literatur mit „hidden hydrogen“ bezeichneten Spezies als H2. Darüber hinaus tragen die beobachteten Umwandlungsprozesse zwischen ortho-H2 und para-H2 sowie die Kopplung an das Phononenspektrum zu einem generellen Verständnis von Wasserstoffmolekülen in Halbleitern bei. Die experimentellen Ergebnisse der LSMn bei 3303 und 3320 cm-1 in Kombination mit Modellrechnungen ergeben einen zugrundeliegenden Defekt mit drei Wasserstoffatomen. Dieser Komplex Y–H3 weist zwei Konfigurationen auf, welche sich durch die Orientierung von nur einer chemischen Bindung unterscheiden. Die Beobachtungen sind mit einer Zinkvakanz besetzt mit drei Wasserstoffatomen bzw. einem Ammoniakmolekül als mikroskopische Struktur gleichermaßen erklärbar. Bisherige Modelle aus der Literatur können damit widerlegt werden. Messungen von Konzentrationsprofilen mit Raman-Spektroskopie offenbaren die lokale Verteilung der Wasserstoffdefekte sowie von Gitterstörungen. An der Oberfläche, im Beisein von Sauerstoffvakanzen, ist HO der dominante flache Donator. In dem sich anschließenden ungestörten Kristallverbund ist hingegen der Donator HBC vorherrschend. In Zentrum, welches von Zinkvakanzen geprägt ist, sind die Konzentrationen von H2 und Y–H3 maximal. In Verbindung mit Temperaturbehandlungen ist eine räumlich aufgelöste Untersuchung der Wechselwirkung möglich

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Demiroglu, Ilker. "Effect of Dimensionality and Polymorphism on the properties of ZnO." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/277286.

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Throughout this thesis, we have studied ZnO and its properties in a bottom-up manner through a dimensionality range starting from 0D nanoparticles to 3D bulk phases. For the 0D clusters and the 2D nanofilms studied we also considered the effect of a support in models designed to study ZnO thin film growth on the Ag(111) surface. In chapter 3, we have studied ZnO nanoclusters on a Ag support and compared their properties with free space ZnO nanoclusters. In this chapter we highlighted the importance of the presence of the support during the global optimization of the clusters (i.e. as opposed to global optimization of the clusters in free space and then introducing a support). Our results show that the presence of the support strongly affects the energetic stability ranking of the nanocluster isomers. More drastically, after a certain cluster size, the support also stabilizes selectively 2D type structures, which are not stable in free space, with respect to the 3D clusters. The extra stabilization of supported 2D clusters is attributed mainly to the contact area, which is evidently greater for 2D clusters where all the atoms can interact with the surface. The importance of the contact are is also observed for 3D clusters, as ellipsoid bubbles or inflated double layer clusters being of lower energy than more spherical clusters on the support whereas the latter, more symmetric 3D clusters are more stable in free space. Matching of the cluster structure with the surface morphology was found to be another factor determining cluster stability. The Zn3O3 sixmembered ring, which is one of the main motifs for both 3D and 2D clusters, matches best with the Ag(111) surface because it follows the same six-fold (C6) symmetry (or its trigonal C3 subgroup with a three-fold axis, taking into account the distinction between Zn and O atoms). However because of the lattice size differences, such matching dies away for larger ZnO clusters. The preferential stabilities of the 2D structures of ZnO clusters can be seen as the initial stages of thin film growth and is found to be in line with the experimentally observed layered ZnO sheets on the Ag(111) surface. In Chapter 4, we have considered a full 2D-ZnO sheet on Ag(111) surface and also investigated also how H atoms interact with it. Following our results for ZnO nanoclusters on the Ag surface, we highlighted the importance of the degree of 2D-ZnO:Ag(111) unit cell commensurability for calculating accurate sheeton-substrate binding energies. We have found a 8:9 commensurate monolayer to be more favored with interatomic potentials and a 7:8 commensurate monolayer with DFT calculations, where the latter is found in experiment. Our calculations showed no evidence of charge transfer or covalent bonding between the Ag(111) surface and the 2D-ZnO sheet, but did show that the ZnO sheet and the Ag(111) surface exhibit small structural distortions in order to maximize their mutual interaction. Calculations of the unsupported 2D-ZnO sheet interacting with hydrogen provided strong evidence for H forming a low energy Zn 4s–H 1s multi center bonding state when passing through a Zn3O3ring of the 2D-ZnO sheet, thus allowing for relatively facile H transport through the sheet. In chapter 5, we have extended our study of supported 2D ZnO nanofilms with higher coverage models, including triangular islands on top of two full monolayers, prepared to model the experimental system. Our results showed that the triangular adlayer islands induce a transition to the WZ structure in the island core and in local region in the two layers immediately below the island core. The islands are also found to have BCT-structured reconstructions on their edges and T1-structured reconstructions on their corners. These models are found to better match the experimental structural data for the experimental 2.7 ML Ag-supported ZnO film with respect to models assuming a purely layered or a purely WZ structure. In chapter 6, we focused on 4ML nanofilms and compared bulk and the 4 ML nanofilm poymorphism of ZnO. Our results revealed that the stability range of nanofilms and their energetic ordering are radically different than that of bulk polymorphs. We have developed a method to generate a wide range of new low energy nanofilm and bulk polymorphs using nets as a basis, and showed that there exist at least three nanofilm structures with trigonal basal plane symmetry compatible epitaxial growth on fcc metal (111) surfaces that are more stable than layered-ZnO. While confirming the previous theoretical studies predicting the BCT-ZnO phase as being the lowest energy free-standing nanofim for small thicknesses, we obtained a range of structurally related and near energetically degenerate phases, indicating there exists BCT polytypism. With increasing thickness we found that atomically reconstructed wz-ZnO becomes more stable than BCT-ZnO for ~14 MLs, and is always more stable than non-reconstructed wz-ZnO. We have also stressed the influence of strain on polymorphism by showing that BCT-ZnO and layered-ZnO nanofilms are unstable to novel polymorphs under in-plane strain. Together with the T1 structures and BCT structures which were also predicted as reconstructions on island corners in the previous chapter, our results strongly suggest that many new nanofilm polymorphs should be experimentally accessible, and in some cases, may have even already been observed. In chapter 7, we focused on bulk polymorphism and, specifically, investigated the effect of nanoporosity. Our results showed that both energetic instability and band gap increase with nanoporosity and we predicted that nanoporosity could induce band gap increases of up to ~1.5 eV relative to wurtzite ZnO. We showed that the band gap increase is related with bandwidth changes in the conduction band and the valance band. We suggested that the underlying physical mechanism for this effect is that introducing nanoporosity, and thus periodic internal void space, restricts extended orbital overlaps and thus decreases bandwidths. Due to the generality of this argument, we expect that nanoporosity could similarly affect bandgap values in a wide range of materials and could be employed as a band gap engineering method.
El treball de recerca desenvolupat en aquesta tesi es centra en ZnO, un dels semiconductors de tipus II-VI amb un ampli ventall d’aplicacions. En les estructures (ZnO)n suportades, s’observa que la presència del suport afecta l’ordre d’estabilitats dels mateixos però de manera molt més dràstica afecta selectivament les estructures bidimensionals (2D) que, a partir d’una certa grandària, en fase gas són menys estables que les tridimensionals (3D). Els càlculs per a la làmina 2D-ZnO aïllada interaccionant amb l’hidrogen proporcionen una forta evidència per a la formació d’un estat d’enllaços multi-centres de baixa energia quan passa a través de l’anell de Zn3O3 de la làmina 2D-ZnO, permetent així de forma relativament fàcil el transport d’hidrogen a través de la làmina. Quan canviem a models amb illes mes grans, observem reconstruccions estructurals a l’interior i sota l’illa formada per una nova capa incompleta. L’interior de les illes triangulars adopta estructura WZ i esta rodejada per vores amb estructures BCT i cantonades amb estructura T1. S’ha observat que aquests models presenten en un millor acord estructural amb les dades experimentals per el cas de les lamines formades per 2.7 ML que no pas respecte als models que assumeixen una estructura purament grafítica o purament WZ. Hem generat un ampli rang de polimorfs de ZnO basats en lamines hexagonals inspirades en l’enumeració de les seves xarxes subjacents característiques i evaluant l’estabilitat del sòlid “bulk” i les nano-lamines d’aquestes estructures mitjançant calculs ab initio. Hem observat un ampli polimorfisme d’estructures de baixa energia en les nano-lamines amb un ordre d’estabilitat totalment diferent al del sòlid “bulk”. A partir d’aquestes bases generals hem pogut tenir un millor coneixement de les transicions estructurals observades durant el creixement epitaxial i les prediccions d’estabilitat de les nano-lamines en variar-ne el gruix i la pressió exercida. Hem conclòs els nostres resultats explicant que la nanoporositat està inextricablement connectada tant amb la Erel com amb el ΔEgap i hem predit que la nanoporositat pot induir un increment en el band gap de fins a ~1.5 eV relatius a la wurtzita ZnO. Comprovant també la generalitat d’aquest fenomen, pe’l CdS i pel CdSe suggerim que la nanoporositat pot ser emprada com un mètode genèric d’enginyeria de band gap per materials funcionals morfològicament i electrònicament.

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Hultqvist, Adam. "Cadmium Free Buffer Layers and the Influence of their Material Properties on the Performance of Cu(In,Ga)Se2 Solar Cells." Doctoral thesis, Uppsala universitet, Fasta tillståndets elektronik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-133112.

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CdS is conventionally used as a buffer layer in Cu(In,Ga)Se2, CIGS, solar cells. The aim of this thesis is to substitute CdS with cadmium-free, more transparent and environmentally benign alternative buffer layers and to analyze how the material properties of alternative layers affect the solar cell performance. The alternative buffer layers have been deposited using Atomic Layer Deposition, ALD. A theoretical explanation for the success of CdS is that its conduction band, Ec, forms a small positive offset with that of CIGS. In one of the studies in this thesis the theory is tested experimentally by changing both the Ec position of the CIGS and of Zn(O,S) buffer layers through changing their gallium and sulfur contents respectively. Surprisingly, the top performing solar cells for all gallium contents have Zn(O,S) buffer layers with the same sulfur content and properties in spite of predicted unfavorable Ec offsets. An explanation is proposed based on observed non-homogenous composition in the buffer layer. This thesis also shows that the solar cell performance is strongly related to the resistivity of alternative buffer layers made of (Zn,Mg)O. A tentative explanation is that a high resistivity reduces the influence of shunt paths at the buffer layer/absorber interface. For devices in operation however, it seems beneficial to induce persistent photoconductivity, by light soaking, which can reduce the effective Ec barrier at the interface and thereby improve the fill factor of the solar cells. Zn-Sn-O is introduced as a new buffer layer in this thesis. The initial studies show that solar cells with Zn-Sn-O buffer layers have comparable performance to the CdS reference devices. While an intrinsic ZnO layer is required for a high reproducibility and performance of solar cells with CdS buffer layers it is shown in this thesis that it can be thinned if Zn(O,S) or omitted if (Zn,Mg)O buffer layers are used instead. As a result, a top conversion efficiency of 18.1 % was achieved with an (Zn,Mg)O buffer layer, a record for a cadmium and sulfur free CIGS solar cell.
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 717

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Tirpak, Olena. "INFLUENCE OF ELECTRON TRAPPING ON MINORITY CARRIER TRANSPORT PROPERTIES OF WIDE BAND GAP SEMICONDUCTORS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3278.

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Minority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning electron microscope results in a significant increase of minority carrier diffusion length. These findings are supported by the cathodoluminescence measurements that demonstrate the decay of near-band-edge intensity as a consequence of increasing carrier lifetime under continuous irradiation by the electron beam. Temperature-dependent measurements were used to determine the activation energies for the electron irradiation-induced effects. The latter energies were found to be consistent with the involvement of deep acceptor states. Based on these findings, the effects of electron irradiation are explained via the mechanism involving carrier trapping on these levels. Solid-state electron injection was also shown to result in a similar increase of minority carrier lifetime and diffusion length. Solid-state injection was carried out by applying the forward bias to a ZnO homojunction and resulted in a significant improvement of the peak photoresponse of the junction. This improvement was unambiguously correlated with the increase of the minority carrier diffusion length due to electron injection.
Ph.D.
Department of Physics
Sciences
Physics PhD

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10

Mokhtari, Abbas. "On the growth, magnetic properties and Magneto-Optical Studies of ZnO based Dilute Magnetic Semiconductors and Magnetite." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500218.

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11

Brandt, Matthias. "Inﬂuence of the electric polarization on carrier transport and recombination dynamics in ZnO-based heterostructures." Doctoral thesis, Universitätsbibliothek Leipzig, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-61074.

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Die vorliegende Arbeit befasst sich mit dem Einfluss der elektrischen Polarisation auf Eigenschaften freier Träger in ZnO basierten Halbleiterheterostrukturen. Dabei werden insbesondere Transporteigenschaften freier Träger sowie deren Rekombinationsdynamik untersucht. Die Arbeit behandelt vier inhaltliche Schwerpunkte. Der erste Schwerpunkt liegt auf den physikalischen Eigenschaften der verwendeten Materialen, hier wird der Zusammenhang der Bandlücke und der Gitterkonstanten von MgZnO Dünnfilmen und deren Magnesiumgehalt beschrieben. Weiterhin wird die Morphologie solcher Filme diskutiert. Auf unterschiedliche Substrate und Abscheidebedingungen wird dabei detailliert eingegangen. Der zweite Schwerpunkt behandelt die Eigenschaften undotierter und phosphordotierter ZnO und MgZnO Dünnfilme. Die strukturellen, Transport- und Lumineszenzeigenschaften werden hier verglichen und Rückschlüsse auf die Züchtungsbedingungen gezogen. Im dritten Schwerpunkt werden Quanteneffekte an ZnO/MgZnO Grenzflaechen behandelt. Hierbei wird insbesondere auf den Einfluss der elektrischen Polarisation eingegangen. Die Präsenz eines zweidimensionalen Elektronengases wird nachgewiesen, und die notwendigen Bedingungen zur Entstehung des sogenannten qunatum confined Stark-effects werden dargelegt. Insbesondere wird hier auf züchtungsrelevante Parameter eingegangen. Den vierten Schwerpunkt stellen Kopplungsphänomene in ZnO/BaTiO3 Heterostrukturen dar. Dabei werden zuerst die experimentell beobachten Eigenschaften verschiedener Heterostrukturen die auf unterschiedlichen Substraten gezüchtet wurden aufgezeigt. Hier stehen strukturelle und Transporteigenschaften im Vordergrund. Ein Modell zur Beschreibung der Ausbildung von Raumladungszonen in derartigen Heterostrukturen wird eingeführt und zur Beschreibung der experimentellen Ergebnisse angewandt. Die Nutzbarkeit der ferroelektrischen Eigenschaften des Materials BaTiO3 in Kombination mit halbleitendem ZnO wurden untersucht. Hierzu wurden ferroelektrische Feldeffekttransistoren unter Verwendung beider Materialien hergestellt. Die prinzipielle Eignung der Bauelemente als nichtflüchtige Speicherelemente wurde nachgewiesen.

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Мухаммед, Абід Аль Карім, Абид Аль Карим Мухаммед, and Abid Al Karim Mukhammed. "Структурные и оптические свойства солнечных элементов на основе пленок ZnO и AIN." Thesis, Вид-во СумДУ, 2012. http://essuir.sumdu.edu.ua/handle/123456789/29538.

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Дисертаційна робота присвячена дослідженню морфології поверхні, структурно-фазового стану, оптичних та електрофізичних властивостей плівок ZnО та AlN, які отримані методами CVD, золь-гель та магнетронним розпиленням, проведено моделювання ВАХ СЕ на основі гетеропереходів n-ZnO/p-Si, n-ZnO/n-CdS/p-Si, n-ZnO/n-CdS/p-CIGS та визначені їх оптимальні фізичні та конструкційні характеристики. Проведено комплексне дослідження структури та субструктури полікристалічних плівок ZnO (ZnО:Al) та AlN залежно від фізико-технологічних умов їх конденсації. Встановлені режими отримання високоякісних конденсатів сполуки, придатних для використання у приладобудуванні. Вивчення електрофізичних властивостей шарів засвідчило, що при підвищенні легування плівок ZnO алюмінієм електропровідність плівок підвищувалася, а питомий опір відповідно зменшувався. Крім того, були чисельно виміряні основні електрофізичні властивості гетеропереходу n- ZnO/p-Si. Проведене чисельне моделювання основних електрофізичних характеристик гетеросистем на основі ZnO, був визначений коефіцієнт корисної дії для кожного з переходів. Вивчений вплив таких параметрів, як товщина поглинального шару, температура конденсації, тип поглинального шару, на поведінку вольт-амперних характеристик та квантового виходу гетеросистем. Було запропоновано та реалізовано моделювання гетеросистем n-ZnO/p-Si, n-ZnO/n-CdS/p-CIGS, n-ZnO/n-CdS/p-Si та n-ZnO/AlN/p-Si. Проведено порівняння модельних та експериментальних результатів. У результаті проведених експериментальних досліджень були визначені оптимальні режими отримання плівок ZnO та AlN, проведений структурно-фазовий аналіз, досліджені оптичні та електрофізичні властивості бездомішкових та легованих алюмінієм плівок оксиду цинку. При порівнянні експериментальних результатів та моделювання було визначено, що введення шару AlN у конструкцію СЕ покращує його характеристики. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/29538
Диссертационная работа посвящена исследованию морфологии поверхности, структурно-фазового состояния, оптических и электрофизических свойств пленок ZnО и AlN, полученных методами CVD, золь-гель и магнетронным распылением. В работе также было проведено моделирование ВАХ солнечных элементов на основе оксида цинка. Проведено комплексное исследование, структуры и субструктуры поликристаллических пленок ZnO (ZnО:Al) и AlN в зависимости от физико-технологических условий их конденсации. Установлены режимы в температурном интервале от 573 до 773 К получения высококачественных конденсатов соединения. Показано, что при повышении температуры конденсации качество пленок заметно возрастает, улучшается их текстура, размер зерна и т. д. Кроме того, полученные в работе пленки ZnO имеют преимущественную текстуру роста (002). Исследование оптических свойств конденсатов показало, что при повышении концентрации алюминия в пленках существенно повышается оптическая ширина запрещенной зоны от 3,25 до 3,65 эВ, что в дальнейшем имеет перспективу применения данного соединения в качестве оконного слоя в тандемных солнечных элементах. Изучение электрофизических свойств слоев показало, что при повышении легирования пленок ZnO алюминием электропроводимость пленок повышалась, а удельное сопротивление соответственно уменьшалось. Кроме того, были численно измерены основные электрофизические свойства гетероперехода n-ZnO/p-Si, такие, как ток короткого замыкания, коэффициент заполнения, коэффициент полезного действия и т. д. Былопредложено и реализовано моделирование гетеросистем n-ZnO/p-Si, n-ZnO/n-CdS/p-CIGS, n-ZnO/n-CdS/p-Si и n-ZnO/AlN/p-Si. Проведено сравнение результаов моделтрования и экспериментальных результатов. Проведено численное моделирование основных электрофизических характеристик гетеросистем на основе ZnO, был определен коэффициент полезного действия для каждого из переходов. Изучено влияние таких параметров, как толщина поглощающего слоя, температура конденсации, тип поглощающего слоя на поведение вольт-амперных характеристик и квантового выхода гетеросистем. Проведено сравнение експериментальных результатов и результатов моделирования, проведена их корреляция. Установлено, что при повышении концентрации алюминия в пленках ZnO ширина запрещенной зоны материала значительно повышается, поэтому такие слои имеют перспективу использования в качестве оконных слоев солнечных элементов. При сравнении экспериментальных результатов и моделирования было определено, что внедрение слоя AlN в конструкцию СЭ улучшает его характеристики. Установлены режимы получения высококачественных конденсатов соединения, пригодных для использования в приборостроении. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/29538
The thesis focuses on investigation of surface morphology, structural and phase state, optical and electro physical properties of ZnO and AlN films, obtained by the following methods: CVD, sol gel, and magnetron sputtering. In this work a modeling of current-voltage characteristics of solar cells based on ZnO was also carried out. In the work the complex investigation of structure and substructure features of polycrystalline ZnO (ZnO:Al) and AlN films was performed. There were determined the modes for obtainment of high-quality compound condensates that can be used in instrument engineering. It was shown that the increase of condensation temperature leads to the increase of film quality, improvement of their texture, grain size etc. Furthermore, the obtained ZnO films have the preferred growth texture (002). The investigation of film electro physical properties showed that the increase of doping of ZnO films by aluminum leads to increase of electrical conductivity, and to decrease of specific resistance. Furthermore, there were defined the basic elec-trophusical properties of n- ZnO/p-Si, hetero junction. During investigation there was proposed and realized a modeling of n-ZnO/p-Si, n-ZnO/n-CdS /p-CIGS, n-ZnO/n-CdS/p-Si and n-ZnO/AlN/p-Si hetero systems. The modeling and experimental results were compared. As a result of conducted experimental researches the optimal modes of ZnO and AlN film obtaining were determined, a structure-phase analysis was carried out, opti-cal and electro physical properties of pure and aluminum-doped ZnO films were in-vestigated. While comparing the modeling and experimental results there was deter-mined that implementation of AlN film into the solar cell structure improves its char-acteristics. It was defined, that the increase of Al concentration ZnO films leads to the increase of band gap of the material, so that such layers can be used as window layers in solar cells. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/29538

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Wang, Lin. "Carrier profiling of ZnO nanowire structures by scanning capacitance microscopy and scanning spreading resistance microscopy." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI031/document.

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Ce travail de thèse porte sur l'application des techniques Scanning Capacitance Microscopy (SCM) et Scanning Spreading Resistance Microscopy (SSRM) pour la caractérisation électrique de nanofils de ZnO avec l'objectif d'en déterminer le dopage par profilage des porteurs libres suite à des essais de dopage de type p. Afin de pouvoir utiliser un référentiel planaire nécessaire à ces mesures par sonde locale, un procédé de remplissage par dip-coating et de polissage a été spécialement développé sur des champs de nanofils quasi-verticaux. De plus, dans le but de parvenir à un étalonnage des mesures SCM et SSRM, nous avons conçu et fait fabriquer des échantillons étalons de dopage de type n, contenant des niveaux de Ga en escalier de densité variable de 2×10^17 à 3×10^20 cm^-3. Les mesures sur des coupes transversales de ces deux de structures multicouches ont permis, pour la première fois sur ZnO d'établir un étalonnage des mesures SCM et SSRM et de déterminer le dopage intrinsèque électriquement actif de couches 2D nanométriques, résultat difficilement atteignable par d'autres techniques d'analyse. Des résultats inattendus de concentration résiduelle de porteur de l'ordre de 2×10^18 et 3×10^18 cm^-3 ont été trouvés sur les nanofils de ZnO crus par MOCVD et par CBD respectivement. Outre la caractérisation électrique microscopique des nanofils par SCM et SSRM, des techniques macroscopiques classiques ont été utilisées pour caractériser des assemblées importantes de nanofils de ZnO. L'origine de la difference entre les résultats de deux genres de technique a été discutée. Nous avons aussi étudié les effets des dopages ex-situ par diffusion du phosphore (procédé SOD) et des dopages in situ par incorporation d'antimoine (Sb) pendant la croissance MOCVD. Les résultats majeurs sont obtenus pour l'antimoine, en utilisant des couches ZnO: Sb 2D et des nanofils cœur-coquille ZnO/ZnO: Sb, ou l'hypothèse d'une compensation partielle du dopage n résiduel par un centre accepteur créé par le dopage Sb semble pouvoir être établie raisonnablement
Based on atomic force microscope (AFM), scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) have demonstrated high efficiency for two dimensional (2D) electrical characterizations of Si semiconductors at nanoscale and then have been extensively employed in Si-based structures/devices before being extended to the study of some other semiconductor materials. However, ZnO, a representative of the third generation semiconductor material, being considered a promising candidate for future devices in many areas, especially in opto-electronic area, has rarely been addressed. Recently, extensive research interests have been attracted by ZnO NWs for future devices such as LED, UV laser and sensor. Therefore, a good understanding of electrical properties of the NWs is in need. In this context, this thesis work is dedicated to the 2D electrical characterization of ZnO NWs with the focus of carrier profiling on this kind of nanostructure in the effort of their p-type doping. For this purpose, a planarization process has been developed for the NWs structure in order to obtain an appropriate sample surface and perform SCM/SSRM measurements on the top of the NWs. For quantitative analysis, Ga doped ZnO multilayer staircase structures were developed serving as calibration samples. Finally, residual carrier concentrations inside the CBD and MOCVD grown ZnO NWs are determined to be around 3×10^18 cm^-3 and 2×10^18 cm^-3, respectively. The results from SCM/SSRM characterization have been compared with that from macroscopic C-V measurements on collective ZnO NWs and the differences are discussed. In addition to carrier profiling on NWs structure, applications of SCM/SSRM on some other ZnO-based nanostructures are also investigated including ZnO:Sb films, ZnO/ZnO:Sb core-shell NWs structure, ZnO/ZnMgO core-multishell coaxial heterostructures

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Доброжан, Олександр Анатолійович, Александр Анатольевич Доброжан, and Oleksandr Anatoliiovych Dobrozhan. "Cтруктурні, оптичні і термоелектричні властивості плівок та наночастинок ZnO, CZTS, CZTSe для фото- і термоперетворювачів." Thesis, Сумський державний університет, 2018. http://essuir.sumdu.edu.ua/handle/123456789/66040.

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Дисертаційна робота присвячена оптимізації основних фотоелектричних характеристик, а саме квантового виходу (Q), густини струму короткого замикання (Jsc), ефективності (η) плівкових ФЕП на основі ГП n-CdS(ZnSe, ZnS)/p-(CZTS, CdTe) із струмознімальними контактами n-ITO(ZnO); дослідженню морфологічних особливостей, структурних, субструктурних, оптичних, термоелектричних властивостей та елементного складу плівок ZnO, CZTS, нанесених методом пульсуючого спрей піролізу, для використання у ФЕП та наноструктурованого матеріалу на основі НЧ CZTSe, синтезованих колоїдним методом, для застосування у ТЕП, що можуть працювати паралельно з ФЕП. Встановлені взаємозв’язки між фізико- та хіміко-технологічними умовами нанесення плівок та синтезу НЧ, наноструктурованого матеріалу на їх основі, та структурними, субструктурними, оптичними, термоелектричними властивостями, елементним складом будуть використані для подальшого створення ФЕП та ТЕП з покращеними характеристиками.
Диссертационная работа посвящена оптимизации основных фотоэлектрических характеристик, а именно квантового выхода (Q), плотности тока короткого замыкания (Jsc), эфективности (η) плёночных ФЭП на основе ГП n-CdS(ZnSe, ZnS)/p-(CZTS, CdTe) с токособирающими контактами ITO(ZnO); исследованию морфологических особенностей, структурных, субструктурных, оптических, термоэлектрических свойств и элементного состава плёнок ZnO, CZTS, нанесённых методом пульсирующего спрей-пиролиза, для применения у вышеуказанных ФЭП и наноструктурированного материала на основе НЧ CZTSe, синтезированных колоидальным методом, для использования у ТЭП, которые могут работать паралельно с ФЭП. Установленные взаимосвязи между физико- и химико-технологическими условиями нанесения плёнок, синтеза НЧ, наноструктурированного материала на их основе, и структурными, субструктурными, оптическими, термоэлектрическими свойствами, элементным составом будут использованы для создания ФЭП и ТЭП с улучшенными характеристиками.
PhD thesis is devoted both to the optimization of basic photoelectric characteristics (quantum yield (Q), density of short circuit current (Jsc), efficiency (η)) of solar cells based on n-CdS(ZnSe, ZnS)/p-(CZTS, CdTe) heterojunctions with n-ITO(ZnO) frontal contacts, and to the investigation of morphological, structural, substructural, optical, thermoelectric properties and chemical composition of: (I) ZnO, CZTS films deposited by spray pyrolysis for application in solar cells; (II) nanostructured materials based on CZTSe nanocrystals synthesized by colloidal method for application in thermoelectric devices which can work simultaneously with solar cells. In the work, modeling approbation was performed by means of investigating the effect of optical and recombination losses on Q, Jsc, η of solar cells based on n-CdS(ZnS)/p-CdTe heterojunctions. Afterwards, the investigation of these losses on the photoelectric characteristics of solar cells based on n-CdS(ZnSe, ZnS)/p-CZTS heterojunctions with n-ITO(ZnO) frontal contacts was carried out with the help of the approbated procedure. Taking into account the results of mathematical modeling, the solar cells based on ZnO frontal contact and CZTS absorber layer were considered. For this purpose, the automated setup for the deposition of ZnO and CZTS films by pulsed spray pyrolysis technique was developed. The in-depth investigation of influence of the main growth conditions of layers’ deposition (substrate temperature (Ts), volume of initial precursor (Vs)) on structural (grains size, phase composition, texture quality, lattice parameters), substructural (coherent scattering domain sizes, level of microdeformations and microstresses, density of dislocations at the boundaries and in the volume of subgrains), optical (transmission coefficients, absorbance, band gap) properties and chemical composition of ZnO, CZTS films, as well as the determination of optimal conditions to obtain the specified films were carried out. Since the solar cells operate at the elevated temperatures, it was proposed to use the additional thermal energy by means of its conversion into electrical energy by use of the thermoelectric devices. For this purpose, the nanostructured thermoelectric material based on CZTSe nanocrystals synthesized by the colloidal method was obtained. The influence of kinetic conditions, namely type of phosphonic acid, on morphological (size, shape), structural (phase composition), optical (absorbance, band gap) properties and chemical composition of CZTSe nanocrystals was determined. The influence of chemical composition on the main thermoelectric properties (concentration (p) and mobility ( u ) of majority charge carriers, relative electrical conductivity ( k ), Seebeck coefficient (SZ)) of nanostructured material based on CZTSe nanocrystals was investigated. The established correlations between the film, nanocrystals growth conditions and structural, substructural, optical, thermoelectric properties, chemical composition will be applied for further development of solar cells and thermoelectric devices with the enhanced characteristics.

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Teran-Escobar, Gerardo, David M. Tanenbaum, Eszter Voroshazi, Martin Hermenau, Kion Norrman, Matthew T. Lloyd, Yulia Galagan, et al. "On the stability of a variety of organic photovoltaic devices by IPCE and in situ IPCE analyses – the ISOS-3 inter-laboratory collaboration." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139279.

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This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPV) devices prepared by leading research laboratories. All devices have been shipped to and degraded at RISØ-DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work, we apply the Incident Photon-to-Electron Conversion Efficiency (IPCE) and the in situ IPCE techniques to determine the relation between solar cell performance and solar cell stability. Different ageing conditions were considered: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The devices were also monitored under conditions of ambient and inert (N2) atmospheres, which allows for the identification of the solar cell materials more susceptible to degradation by ambient air (oxygen and moisture). The different OPVs configurations permitted the study of the intrinsic stability of the devices depending on: two different ITO-replacement alternatives, two different hole extraction layers (PEDOT:PSS and MoO3), and two different P3HT-based polymers. The response of un-encapsulated devices to ambient atmosphere offered insight into the importance of moisture in solar cell performance. Our results demonstrate that the IPCE and the in situ IPCE techniques are valuable analytical methods to understand device degradation and solar cell lifetime
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

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Frenzel, Heiko. "ZnO-based metal-semiconductor field-effect transistors." Doctoral thesis, Universitätsbibliothek Leipzig, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-61957.

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Die vorliegende Arbeit befasst sich mit der Entwicklung, Herstellung und Untersuchung von ZnO-basierten Feldeffekttransistoren (FET). Dabei werden im ersten Teil Eigenschaften von ein- und mehrschichtigen Isolatoren mit hohen Dielektrizitätskonstanten betrachtet, die mittels gepulster Laserabscheidung (PLD) dargestellt wurden. Die elektrischen und kapazitiven Eigenschaften dieser Isolatoren innerhalb von Metall-Isolator-Metall (MIM) bzw. Metall-Isolator-Halbleiter (MIS) Übergängen wurden untersucht. Letzterer wurde schließlich als Gate-Struktur in Metall-Isolator-Halbleiter-FET (MISFET) mit unten (backgate) bzw. oben liegendem Gate (topgate) genutzt. Der zweite Teil konzentriert sich auf Metal-Halbleiter-FET (MESFET), die einen Schottky-Kontakt alsGate nutzen. Dieser wurde mittels reaktiver Kathodenzerstäubung (Sputtern) von Ag, Pt, Pd oder Au unter Einflußvon Sauerstoff hergestellt. ZnO-MESFET stellen eine vielversprechende Alternative zu den bisher in der Oxid-basierten Elektronik verwendeten MISFET dar. Durch die Variation des verwendeten Gate-Metalls, Dotierung, Dicke und Struktur des Kanals und Kontakstruktur, wurde ein Herstellungsstandard gefunden, der zu weiteren Untersuchungen herangezogen wurde. So wurde die Degradation der MESFET unter Belastung durch dauerhaft angelegte Spannung, Einfluss von Licht und erhöhten Temperaturen sowie lange Lagerung getestet. Weiterhin wurden ZnO-MESFET auf industriell genutztem Glasssubstrat hergestellt und untersucht, um die Möglichkeit einer großflächigen Anwendung in Anzeigeelementen aufzuzeigen. Einfache integrierte Schaltungen, wie Inverter und ein NOR-Gatter, wurden realisiert. Dazu wurden Inverter mit sogenannten Pegelschiebern verwendet, welche die Ausgangsspannung des Inverters so verschieben, dass eine logische Aneinanderreihungvon Invertern möglich wird. Schließlich wurden volltransparente MESFET und Inverter, basierend auf neuartigen transparenten gleichrichtenden Kontakten demonstriert.

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Teran-Escobar, Gerardo, David M. Tanenbaum, Eszter Voroshazi, Martin Hermenau, Kion Norrman, Matthew T. Lloyd, Yulia Galagan, et al. "On the stability of a variety of organic photovoltaic devices by IPCE and in situ IPCE analyses – the ISOS-3 inter-laboratory collaboration." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27818.

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This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPV) devices prepared by leading research laboratories. All devices have been shipped to and degraded at RISØ-DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work, we apply the Incident Photon-to-Electron Conversion Efficiency (IPCE) and the in situ IPCE techniques to determine the relation between solar cell performance and solar cell stability. Different ageing conditions were considered: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The devices were also monitored under conditions of ambient and inert (N2) atmospheres, which allows for the identification of the solar cell materials more susceptible to degradation by ambient air (oxygen and moisture). The different OPVs configurations permitted the study of the intrinsic stability of the devices depending on: two different ITO-replacement alternatives, two different hole extraction layers (PEDOT:PSS and MoO3), and two different P3HT-based polymers. The response of un-encapsulated devices to ambient atmosphere offered insight into the importance of moisture in solar cell performance. Our results demonstrate that the IPCE and the in situ IPCE techniques are valuable analytical methods to understand device degradation and solar cell lifetime.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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Chaganti, Venkata R. "Study of the structural and spectroscopic properties of small ZnS clusters by DFT." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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19

Dobson, Stephen Robert. "Development of polymer templates for ZnO nanorods." Thesis, Nelson Mandela Metropolitan University, 2014. http://hdl.handle.net/10948/d1020805.

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One of the biggest challenges for the semiconductor industry is the development of nanofabrication techniques that allow for the fabrication of structures on a scale tens of nanometers in size. This provides greater potential functionality at reduced costs. Established conventional techniques, such as photolithography, are unable to achieve features below 30 nm due to the inherent limitations of the wavelength of light sources currently available. For this reason block copolymers received considerable attention in order to overcome these challenges in lithographic technology. Block copolymers have an inherent processing advantage of self assembling into various nanoscopic structures such as spheres, cylinders and lamellae amongst others on a scale below 50 nm. The dimensions and structures are readily tuneable based on molecular weights (Mw) and compositions of the copolymers. However, to be usable within industry a great deal more research still needs to be conducted on the use and nature of block copolymers. In this study the block copolymer of poly(styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask for semiconductor growth. Research was conducted on thin films of PS-b-PMMA by altering the parameters influencing the kinetics and thermodynamic effects on the thin films, in order to produce a structure of cylinders of PMMA perpendicular to the substrate within a PS matrix on a silicon (Si) substrate. It is shown that thermally annealing the PS-b-PMMA thin films under conditions where there is no preferential interaction of the substrate or open surface with either components of the block copolymer (i.e. PS or PMMA with Si or ambient) and at an appropriate thin film thickness, perpendicular cylinders of PMMA within a PS matrix form in the thin films. The determined ideal thin film thickness is 32 nm, with non-preferential interaction attained between block and substrate by coating a poly(styrene-random-methylmethacrylate) (PS-r-PMMA) on the Si substrate and annealing within a vacuum. Additionally, acetic acid, as a known selective solvent of PMMA, is used to further process the thin film of PS-b-PMMA. Thus a final PS nano-mask containing pores with a diameter tens of nanometers in size is produced. The pores are shown to have an average diameter of 13.5 nm. Measurements were taken throughout the investigation using a scanning probe microscope (SPM) to determine surface topography and phase morphology of the PS-b-PMMA thin films. X-ray reflectometry (XRR) is used to measure film thickness. The research in this study shows that thin films of PS containing hexagonally arranged pores can be produced and could find potential use as a nano-mask for semiconductor growth.

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Kalusniak, Sascha. "Ultraviolet and visible semiconductor lasers based on ZnO heterostructures." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16898.

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Im Rahmen dieser Arbeit wurden die optischen Eigenschaften von auf ZnO-basierenden Heterostrukturen untersucht. Besonderes Augenmerk lag hierbei auf ihrer Eignung als aktives Material in Laserdioden für den ultravioletten und sichtbaren Spektralbereich. Es wurde gezeigt, dass ZnO und seine ternären Mischkristalle ZnCdO und ZnMgO erstaunlich vielfältige Anwendungen ermöglichen. Mit diesem Materialsystem lässt sich sowohl ein sehr großer Spektralbereich für Lasertätigkeit abdecken als auch eine Vielzahl von Laseranordnungen realisieren. Im Detail wurde demonstriert, dass sich die Lasertätigkeit von ZnCdO/ZnO Quantengraben-Strukturen vom violetten bis in den grünen Spektralbereich verschieben lässt. Obwohl diese Strukturen starke interne elektrische Felder aufweisen, konnte optisch gepumpte Lasertätigkeit bei Zimmertemperatur bis zu einer Wellenlänge von 510 nm gezeigt werden. Die für die Lasertätigkeit nötige optische Rückkopplung wird durch makroskopische Defekte der Probe verursacht und die Proben fungieren somit als Zufallslaser. Die Herstellung von Mikroresonatoren ermöglichte die Untersuchung des Zusammenspiels von Fabry-Perot- und Zufalls-Rückkopplung. Die experimentellen und theoretischen Ergebnisse zeigen, dass der Schwellengewinn eines Zufallslasers in der Regel größer ist als der des Fabry-Perot-Lasers. Des Weiteren wurde gezeigt, dass hoch reflektierende Braggreflektoren für den ultravioletten und blau/grünen Spektralbereich aus ZnO- und ZnMgO-Schichten hergestellt werden können. Ferner wurden die teils unbekannten Brechungsindexverläufe der verwendeten ternären Materialen erarbeitet und Mikrokavitäten mit ZnO/ZnMgO Quantengraben Strukturen als aktive Schichten realisiert. An diesen Kavitäten konnte bei Temperaturen bis zu 150 K starke Kopplung zwischen Exzitonen und Photonen nachgewiesen werden. Bei Zimmertemperatur konnte vertikal-emittierende Lasertätigkeit im nahen ultravioletten Spektralbereich demonstriert werden.
In the framework of this thesis, the optical properties of ZnO-based heterostructures fabricated by molecular beam epitaxy have been investigated, particularly with regard to their suitability for semiconductor laser devices operating in the ultraviolet and visible spectral range. It turned out that ZnO and its ternary alloys ZnMgO and ZnCdO are extremely versatile. They allow to tune the laser emission in a wide spectral range as well as to realize various laser geometries. In detail, it was shown that the laser emission of ZnCdO/ZnO multiple quantum wells can cover a spectral range from violet to green wavelengths. Although these structures suffer from large built-in electric fields, room temperature laser action under optical pumping was demonstrated up to a wavelength of 510. The optical feedback for lasing is provided by growth imperfections on a macroscopic length scale turning these structures into random lasers. The fabrication of micro-resonators allowed to study the interplay between random and Fabry-Perot feedback. The experimental and theoretical analysis shows that random feedback generally requires a larger gain than under Fabry-Perot feedback. Further, this work demonstrates that ZnO- and ZnMgO-layers can be used to fabricate highly reflective distributed Bragg reflectors for applications in the ultraviolet and blue/green spectral range. The partly unknown dispersion curves of the index of refraction of the employed ternary alloys have been elaborated. This enabled the realization of all monolithic microcavities with ZnO/ZnMgO quantum wells as active zone. For temperatures below 150 K strong exciton-photon coupling is observed in such microcavities. At room temperature, vertical cavity surface emitting laser action in the near UV spectral range is demonstrated for appropriately designed microcavities.

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Shi, Shenlei. "Exciton related optical properties of ZnO." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38284881.

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Bunzli, Christa. "Photoelectrichemical properties of nanostructured ZnO electrodes." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.547847.

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23

Schuler, Leo Pius. "Properties and Characterisation of Sputtered ZnO." Thesis, University of Canterbury. Electrical and Computer Engineering, 2008. http://hdl.handle.net/10092/1900.

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The aim of this work was the study of sputtered zinc oxide (ZnO) film deposition, the optimisation and characterisation of film properties and applications as a sensing material. In recent years there has been increased interest in ZnO in terms of its potential applications as piezoelectric films (or coatings) for surface acoustic wave devices (SAW), for IR and visible light emitting devices and UV sensing. The electrical, optoelectronic and photochemical properties of undoped ZnO have resulted in its use for solar cells, transparent electrodes and blue/UV light emitting devices. ZnO is a unique material that exhibits both semiconducting and piezoelectric properties. In the past decade, numerous studies have been made on both production and application of one-dimensional ZnO. Compared with other semiconductor materials, ZnO has a higher exciton binding energy of 60 meV, which gives it a high potential for room temperature light emission, is more resistant to radiation, and is multifunctional as it has piezoelectric, ferroelectric, and ferromagnetic properties. ZnO-based semiconductor and nanowire devices are also promising for the integration on a single chip. So far, the various applications of ZnO nanomaterials such as biosensors, UV detectors and field emission displays are being developed. In this work, ZnO was sputtered using both DC and RF magnetron sputtering. Reactive DC sputtering was performed with a Zn target and oxygen plasma, while RF sputtering was performed with a ZnO target. Comparisons between films deposited under different conditions on different substrates were employed to assess film properties. Several experiments were performed on as-grown films as a control for subsequence treatments, other samples were post-annealed in N2 at temperatures up to 1200 ºC, the highest reported annealing temperature and the quality of the deposited films was determined using PL, RBS, XRD, SEM and AFM. The piezoelectric properties (d33) of selected films were determined using single beam interferometry, double beam interferometry, and for the first time, using piezoelectric force microscopy (PFM). It was found that DC sputtered films yielded better quality films as evident by PL and XRD analysis and higher piezoelectric response than RF sputtered films. Films deposited using DC sputtering on Si substrates and followed by post-annealing in N2 atmosphere at 1100 ºC showed the highest recorded PL response, while films deposited on sapphire showed good PL response without any need for post-annealing. The d33 of selected films were determined first using single beam interferometry and inflated results were reported, caused by sample bending/buckling. Double beam interferometry results confirmed d33 values in the range of 3.3 to 4.3 pm/V. Piezoelectric force microscopy (PFM) which is based on AFM, was employed to investigate the local electromechanical (piezoelectric) properties of the ZnO films. UV sensing was demonstrated using Schottky contacts and SAW devices on ZnO deposited on Si and post-annealed. In the first instance, Schottky contacts were fabricated on the films and the I V characteristics determined under exposure of various light sources. The current increased up to one order of magnitude during exposure with a halogen light bulb, which is known to emit energy in the UV band. Another experiment was performed using surface acoustic wave (SAW) devices which were fabricated on the films and interrogated using a network analyser. These SAW devices contain an interdigitated transducer and two reflectors each. The signals sent back from the two reflectors were analysed under various light conditions and gave lower readings during exposure to UV light. In order to enable device fabrication of UV sensors a novel “super coating”, achieving both optimised PL and d33 properties, was designed, fabricated and tested. The structure is based on optically transparent Quartz substrate. During this experiment the first DC sputtered coat was optimised to have high PL response by post-annealing at 900 ºC. Afterwards, the second coat was left as-sputtered in order to have highly piezoelectric properties. Preliminary analysis using XRD showed two peaks corresponding to the annealed and not annealed coat, which suggest the super coating combines the properties of the two individual films. This configuration has the potential to be used as UV sensing material and as piezoelectric substrate for SAW devices.

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Shi, Shenlei, and 施申蕾. "Exciton related optical properties of ZnO." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38284881.

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Bohorquez, Ballen Jaime. "Thermal transport in low dimensional semiconductor nanostructures." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/798.

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We have performed a first principles density functional theory (DFT) calculations to study the thermal conductivity in ZnO nanotubes, ZnO nanowires, and Si/Ge shell-core nanowires. We found the equilibrium configuration and the electric band structure of each nanostructure using DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach using a Green's function method. All ZnO nanostructures studied exhibit semiconducting behavior, with direct bandgap at the Gamma point. The calculated values for the bandgaps were larger than the value of the bandgap of the bulk ZnO. We were able to identify phonon modes in which the motion of Zn atoms is significant when it is compared with the motion of oxygen atoms. The thermal conductivity depends on the diameter of the nanowires and nanotubes and it is dramatically affected when the nanowire or nanotube is doped with Ga. For Si/Ge nanowires, the slope and the curvature of acoustic modes in the phonon dispersion relation increases when the diameter increases. For nanowires with the same number of atoms, the slope and curvature of acoustic modes depends on the concentration of Si atoms. We were able to identify phonon modes in which the motion of core atoms is significant when it is compared with motion of atoms on the nanowire's shell. The thermal conductivity in these nanostructures depends on the nanowire's diameter and on the Si atoms concentration.

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Tallarida, Massimo. "Electronic properties of semiconductor surfaces and metal, semiconductor interfaces." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/196/index.html.

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27

Subannajui, Kittitat [Verfasser], and Margit [Akademischer Betreuer] Zacharias. "ZnO nanowires : : fabrication, properties and devices = ZnO-Nanodrähten Herstellung : Eigenschaften und Devices." Freiburg : Universität, 2011. http://d-nb.info/112346040X/34.

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Li, Fang. "Microstructural properties of semiconductor nanostructures." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:396024e1-a646-40ca-8212-cad925b18311.

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Semiconductor nanostructures have attracted great interest owing to their unique physical properties and potential applications in nanoscale functional devices. The enhancement of the physical properties of semiconductor nanostructures and their performance in devices requires a deeper understanding of their fundamental microstructural properties. Thus this thesis is focused on the experimental and theoretical studies of the microstructural properties of two important semiconductor nanostructures: axial heterostructured silicon nanowires with varying doping and indium nitride colloidal nanoparticles. In this thesis, axial heterostructured silicon nanowires with varying doping were synthesized on an oxide-removed Si{111} substrate using a vapour-liquid-solid approach. Their fundamental microstructural properties, including the crystalline structure, wire growth direction and morphologies, were studied using various characterization techniques. It is found that a very small fraction of the silicon nanowires crystallize in a hexagonal (wurtzite) phase, which is thermodynamically unstable in bulk silicon under ambient conditions, while a large majority of the synthesized silicon nanowires exhibit the expected diamond cubic crystalline structure. About 75% of the diamond cubic silicon nanowires synthesized grow in a single <111> direction, while the rest contain growth-related kinks, where the nanowire switches to another direction during the growth. The ~109° silicon nanowire kinks are the most commonly observed, and the growth direction before and after such ~109° kink are both <111>. The sidewalls of silicon nanowires do not change abruptly at the ~109° kink, but exhibit an elbow-shaped structure. It is also found that the nanowire sidewalls exhibit periodic nanofaceting, which is strongly doping-dependent. The nanofaceting is found to occur during the enhanced sidewall growth that arises when the diborane dopant gas is introduced. A thermodynamic model predicting the dependence of nanofacet period on the wire diameter is developed. Another semiconductor nanostructure studied in this thesis is indium nitride colloidal nanoparticles, which were grown using a solution-phase chemical method. The formation of such indium nitride colloidal nanoparticles is confirmed by studying their compositions, crystalline structures and shape using various electron microscopy techniques. The size of the indium nitride colloidal nanoparticles was controlled by varying the time of solution-phase reactions. The most probable size of the colloidal nanoparticles increases and the size distribution broadens with the increase of reaction time. The crystalline structures of the indium nitride colloidal nanoparticles are found to be particle size dependent. The observed dependence of the band gap blueshift of the indium nitride colloidal nanoparticles on the reaction time (hence the particle size) is explained by the quantum-size effect.

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29

Yee, Wai Mun. "Spectral properties of semiconductor lasers." Thesis, University of Bath, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240689.

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Schlenker, Eva. "ZnO based nanostructures properties and device applicability." Göttingen Cuvillier, 2009. http://d-nb.info/996748695/04.

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31

Yang, Li-Li. "Synthesis and Optical Properties of ZnO Nanostructures." Licentiate thesis, Linköping University, Linköping University, Department of Science and Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15535.

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One-dimensional ZnO nanostructures have great potential applications in the fields of optoelectronic and sensor devices. Therefore, it is really important to realize the controllable growth of one-dimensional ZnO nanostructures and investigate their properties. The main points for this thesis are not only to successfully realize the controllable growth of ZnO nonawires, nanorods and quantum dots (QDs), and also investigate the structure and optical properties in detail by the methods of scan electron microscope(SEM), transmission electron microscope(TEM), resonant Raman, photoluminescence(PL) and low-temperature time resolved PL spectrum.

to grown ZnO nanorod arrays (ZNAs) on Si substrates. Firstly, the effects of ZnO nanoparticles, pH value of chemical solution, angel θ between substrate and beaker bottom on the structures of the samples were symmetrically investigated and the optimized growth condition to grow ZNAs can be concluded as follows: seed layer of ZnO nanoparticles, pH=6 and θ=70°. On the basis of these, the diameter of ZNAs was well controlled from 150nm~40nm through adjusting the diameter and density of the ZnO nanoparticles pretreated on the Si substrates. The experimental results indicated that both diameter and density of ZnO nanoparticles on the substrates determined the diameter of ZNAs. But when the density is higher than the critical value of 2.3×10⁸cm^-2, the density will become the dominant factor to determine the diameter of ZNAs.

One the other hand, the optical properties of ZNAs were investigated in detail. The Raman and photoluminescence (PL) results showed that after an annealing treatment around 500oC in air atmosphere, the crystal structure and optical properties became much better due to the decrease of surface defects. The resonant Raman measurements excited by 351.1nm not only revealed that the surface defects play a significant role in the as-grown sample, but also suggested that the strong intensity increase of some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defects scattering contribution for ZnO nanorods annealed from 500°C to 700°C. It is the first time to the best of our knowledge that the Raman measurements can be used to monitor the change of surface defects and deep level defects in the CBD grown ZnO nanorods. We have also presented, for the first time, a time resolved PL study in CBD grown ZnO nanorods with different diameters. The results show that the decay time of the excitons in the nanorods strongly depends on the diameter of the nanorods. The altered decay time is mainly due to the surface recombination process. The effective time constant related to the surface recombination velocity was deduced. A thermal treatment under 500°C will suppress the surface recombination channel, resulting in an improvement of the optical quality for the ZnO nanorods.

This thesis not only provides the effective way to control the size of ZNAs, but also obtains some beneficial results in aspects of their optical properties, which builds theoretical and experimental foundation for much better and broader applications of one-dimensional ZnO nanostructures.

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Yang, Li Li. "Synthesis and optical properties of ZnO nanostructures /." Norrköping : Department of Science and Technology, Linköping University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15535.

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33

CHEN, HONG-REN, and 陳宏仁. "The study of electrical properties of the ZnO semiconductor." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/35476340646320326853.

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Hu, Chia-Yen, and 胡嘉晏. "Growth and Physical Properties of ZnO Semiconductor on Perovskite Oxides." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/21487079699147997893.

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碩士
國立臺灣海洋大學
材料工程研究所
100
This study synthesizes the ZnO nanostructures on the ultrathin ZnO, Au, and Ag layers coated (100) SrTiO3 (STO) single-crystal substrates via thermal evaporation. The effects of various ultrathin layers on the growth of ZnO nanostructures were discussed. ZnO nanostructures grown on the bare STO substrate have a mixed feature of sheet and wire. Those grown on the ZnO-, Au-, and Ag-coated STO substrates exhibit a wire feature. X-ray diffraction patterns and scanning electron microscopy images show that the Au and Ag catalyst layers substantially enhanced the growth of c-axis-oriented ZnO crystals on the (100) STO substrates. Among various substrates (Au/STO, Ag/STO, ZnO/STO, Au/ZnO/STO, and Ag/ZnO/STO), the ZnO nanostructurs grown on the Au/STO are highly c-axis-oriented over the area of interest. The intensity ratio of UV to visible emission bands reached 55; this reveals the as-grown ZnO nanostructures are of highly crystalline quality. The P-type La0.67Sr0.33MnO3 (LSMO) thin films with various thicknesses (50, 100, and 150 nm) were coated on the (100) STO single crystals to grow N-type ZnO nanostructures. Characterization of ZnO/LSMO heterostructures was investigated. The experimental results show that the ZnO/LSMO heterostructures with various LSMO thicknesses thin films have a nonlinear current-voltage characteristic. Moreover, the heterostructure formed on the 950oC annealed LSMO thin film exhibits the enhanced electrical rectifying characteristics. The use of Ag as metal catalyst on the LSMO thin films to grow ZnO nanostructures will results in the Ag metal residual at the hetero-interface. This might cause the linear current-voltage characteristics of the ZnO/LSMO heterostructures.

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茅一超. "Optical Properties of ZnO-SiO2 and ZnO-SiNx Semiconductor-doped Glass Thin Films Prepared by Sputtering Method." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/25019660852926674115.

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碩士
國立交通大學
材料科學與工程系所
94
The target-attachment sputtering method was adopted to prepare the ZnO-SiNx semiconductor-doped glass (SDG) samples (called ZSN system) and their luminescence properties, composition and microstructures were characterized. The experimental results of ZSN system were compared with those of ZnO-SiO2 SDG samples (called ZSO system) obtained previously so that the luminance properties of nano-sized ZnO particles embedded in different matrixes can be understood. As revealed by TEM analysis, spherical ZnO nanoparticles about 5 ~ 10 nm in diameter uniformly dispersed in both matrices when doping concentrations were low. In ZSN system, the ZnO microstructure changed from discrete particles to typical column-like phase when the chip-to-target area ratio exceeded 22.68%. The ESCA analysis indicated that in ZnO lattice the charge status of Zn is Zn2+, and as to O element, it becomes O2�{ in ZnO lattice and in amorphous matrixes or incompletely bonded or absorbed O. In the part of luminance properties, three emission bands, the yellow-green, blue and UV (ultra-violet) emissions were observed in the ZSO and ZSN samples. In ZSO system, the oxygen vacancies were the emission centre of yellow-green luminescence; the presence of the blue emission was attributed to the large number of ZnO/SiO2 interfaces which enlarges the depletion layer width and then amplifies the transition from conduction band (CB) to the zinc vacancies ( ) level. In ZSO system, the intensity of green/yellow emission increased with the ZnO content, while the intensity of blue emission behaved oppositely. The mechanism of green/yellow emission in ZSN system was the same as that of ZSO system. As to the blue emission in ZSN system, two possible mechanisms were deduced. One is the transition from CB to the impurity acceptor levels induced by the p-type nitrogen doping in ZnO. The other is related to the CB-to- transition due to the depletion layer enlargement resulted from the increase of acceptor density. The intensities of blue emissions in system ZSN could be modulated by ZnO content, however, it increased with the increase of ZnO doping concentration in contrast to ZSO system.

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Chung-WeiLiu and 劉宗維. "Optoelectronic and Structure Properties of Diluted Magnetic Semiconductor Based on ZnO Nanorods." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/tcf4te.

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博士
國立成功大學
微電子工程研究所
102
In this dissertation, in order to improve structure quality, the ZnO-based nanorods were fabricated by two processes, including annealing treatment and doping method. Transition-metal-doped (TM-doped) ZnO ultraviolet (UV) photodetectors (PDs) were also studied. This dissertation is divided into four parts; the first of which investigates the surface quality of ZnO nanorods. The second part discusses the growth of TM-doped ZnO nanorods, and the third part analyzes the effect of doping concentration on the bulk quality of TM-doped ZnO nanorods. The final part discusses TM-doped ZnO UV PDs. To begin with, the surface quality of ZnO nanorods, which were grown in aqueous solution. After post-annealing, ZnO nanorods were analyzed by second harmonic generation (SHG) with the assistance of photoluminescence (PL) spectroscopy and the X-ray photoelectron (XPS) spectroscopy. SHG is sensitive to the quality of surface structure and involves the elimination of surface defects and restructuring. Oxygen (O)-deficient and surface defects were generated during the growth of ZnO nanorods. PL and XPS analyses results indicated that the surface defects on the nanorods were reduced at annealing temperatures above 600 °C. The bulk crystal structure was repaired for high activation temperatures (〉 700 °C) based on X-ray diffraction (XRD) results. The SHG results revealed the relationship between surface restructuring of ZnO nanorods and annealing temperature. Then, room-temperature ferromagnetism (RTFM) was observed in Co-doped ZnO (Co:ZnO) and Fe-doped ZnO (Fe:ZnO) vertically aligned nanorod arrays that were grown via hydrothermal synthesis. The evolution of RTFM properties and nanorod qualities were studied at different growth temperatures and doping concentrations. At the growth temperature of 80 °C, the vertically aligned ZnO nanorods were well-formed; Co or Fe was readily substituted for Zn in the nanorod arrays. The weak RTFM of Co:ZnO and Fe:ZnO nanorod arrays was determined via magnetization measurements. The morphology and quality of the nanorods were examined using structure and composition analysis tools. Co or Fe atoms were readily incorporated into the ZnO lattice without any precipitation or segregation of the secondary phase in vertically aligned ZnO nanorod arrays. The properties of the nanorods were enhanced at low doping concentrations (1%) at the growth temperature of 80 °C. Furthermore, high-quality ZnO nanorods that were free from post-annealing treatment were fabricated via low-temperature hydrothermal synthesis by using dilute Co dopants. Detailed analyses on the bulk quality of ZnO nanorods were performed with SHG via XRD and PL. SHG provided a more sensitive differentiation between nanostructures and thin films compared with XRD. The structure of ZnO nanorods shows a high surface-to-volume ratio, which resulted in large surface dipole moments in the radial direction of the nanorods. Moreover, high variations in the gradient of the electrical field were observed around the nanorod structure enhancing the SHG signal. ZnO nanorods with dilute Co-doping concentrations (1%) exhibited a higher bulk crystal quality than pure ZnO nanorods and those with high doping concentrations. Finally, Co:ZnO and Fe:ZnO nanorod metal-semiconductor-metal (MSM) UV PDs were fabricated with respective ratios of UV-to-visible rejection of 11700 and 25000 upon biasing at 1 V with a sharp cutoff at 380 nm. Moreover, the dark and photo noise equivalent power (NEP) of the fabricated Co:ZnO nanorod MSM PDs were 1.3 × 10−13 and 1.8 × 10−11 W at corresponding dark detectivities (D*) and photo D* of 1.1×1014 and 7.3×1011 cm•Hz0.5•W-1, respectively. Co:ZnO nanorod UV PDs exhibited lower dark currents and better flicker noise characteristics compared with ZnO nanorod PDs.

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37

Viswanatha, Ranjani. "Growth Kinetics And Electronic Properties Of Semiconducting Nanocrystals In The Quantum Confined Regime." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/403.

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Properties of nanocrystals are extremely sensitive to their sizes when their sizes are smaller or of the order of the excitonic diameter due to the quantum confinement effect. The interest in this field has been concentrated basically in understanding the size-property relations of nanocrystals, for example, the pronounced variation in the bandgap of the material or the fluorescence emission properties, by tuning the sizes of the nanocrystals. Thus, the optical and electronic properties of semiconductor nanocrystals can be tailor-made to suit the needs of the specific application and hence is of immense importance. One of the major aspects necessary for the actual realization of the various applications is the ability to synthesize nanocrystals of the required size with a controlled size distribution. The growing demand to obtain such nanocrystals with the required size and controlled size distribution is met largely by the solution route synthesis of nanocrystals, that constitutes an important class of synthesis methods due to their ease of implementation and the high degree of flexibility. The main difficulty of this method is that the dependence of the average size and the size distribution of the generated particles on parameters of the reaction are not understood in detail and therefore, the optimal reaction conditions are arrived at essentially in an empirical and intuitive manner. From a fundamental point of view, understanding the growth kinetics of various nanocrystals can provide a deeper insight into the phenomena. The study of growth kinetics can be experimentally achieved by measuring the time evolution of diameter using several in-situ techniques like UV-absorption and small angle X-ray scattering. Having understood the mechanism of growth of nanocrystals, it is possible to obtain the required size of the nanocrystal using optimized synthesis conditions. The properties of these high quality nanocrystals can be further tuned by doping with a small percentage of magnetic ions. The optical and magnetic properties of these nanocrystals play an important role in the various technological applications. The ﬁrst part of the thesis concentrates on the theoretical methods to study the electronic structure of semiconductor nanocrystals. The second part describes the studies performed on growth of various nanocrystal systems, both in the presence and absence of capping agents. The third part of the thesis describes the studies carried out on ZnO and doped ZnO nanocrystals, synthesized using optimal conditions that were obtained in the earlier part of the thesis. The thesis is divided into five chapters which are described below. Chapter 1 provides a brief overall perspective of various interesting properties of semiconductor nanocrystals, including various concepts relevant for the study of such systems. Chapter 2 describes experimental and theoretical methods used for the study of nanocrystals reported in this thesis. In Chapter 3 of this thesis, we report results of theoretical studies carried out on III-V and II-VI semiconductors using the tight-binding (TB) methodology. Chapter 4 presents the investigations on the growth kinetics of several nanocrystal systems. Chapter 5 presents experimental investigations carried out on undoped and various transition metal (TM) doped ZnO nanocrystals. In summary, we have performed electronic structure calculations on various nanocrystal systems, devised a novel method to obtain the size distribution from UV-absorption spectrum and studied the mechanism of growth in the presence and absence of capping agents in various II-VI semiconductors. Using the optimal conditions obtained from the growth studies, we prepare high quality ZnO nanocrystals of required size, both in free-standing and capped states and doped it with small percentages of various transition metals like Mn, Cu and Fe. We have then studied their optical and magnetic properties.

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38

Viswanatha, Ranjani. "Growth Kinetics And Electronic Properties Of Semiconducting Nanocrystals In The Quantum Confined Regime." Thesis, 2006. http://hdl.handle.net/2005/403.

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Abstract:

Properties of nanocrystals are extremely sensitive to their sizes when their sizes are smaller or of the order of the excitonic diameter due to the quantum confinement effect. The interest in this field has been concentrated basically in understanding the size-property relations of nanocrystals, for example, the pronounced variation in the bandgap of the material or the fluorescence emission properties, by tuning the sizes of the nanocrystals. Thus, the optical and electronic properties of semiconductor nanocrystals can be tailor-made to suit the needs of the specific application and hence is of immense importance. One of the major aspects necessary for the actual realization of the various applications is the ability to synthesize nanocrystals of the required size with a controlled size distribution. The growing demand to obtain such nanocrystals with the required size and controlled size distribution is met largely by the solution route synthesis of nanocrystals, that constitutes an important class of synthesis methods due to their ease of implementation and the high degree of flexibility. The main difficulty of this method is that the dependence of the average size and the size distribution of the generated particles on parameters of the reaction are not understood in detail and therefore, the optimal reaction conditions are arrived at essentially in an empirical and intuitive manner. From a fundamental point of view, understanding the growth kinetics of various nanocrystals can provide a deeper insight into the phenomena. The study of growth kinetics can be experimentally achieved by measuring the time evolution of diameter using several in-situ techniques like UV-absorption and small angle X-ray scattering. Having understood the mechanism of growth of nanocrystals, it is possible to obtain the required size of the nanocrystal using optimized synthesis conditions. The properties of these high quality nanocrystals can be further tuned by doping with a small percentage of magnetic ions. The optical and magnetic properties of these nanocrystals play an important role in the various technological applications. The ﬁrst part of the thesis concentrates on the theoretical methods to study the electronic structure of semiconductor nanocrystals. The second part describes the studies performed on growth of various nanocrystal systems, both in the presence and absence of capping agents. The third part of the thesis describes the studies carried out on ZnO and doped ZnO nanocrystals, synthesized using optimal conditions that were obtained in the earlier part of the thesis. The thesis is divided into five chapters which are described below. Chapter 1 provides a brief overall perspective of various interesting properties of semiconductor nanocrystals, including various concepts relevant for the study of such systems. Chapter 2 describes experimental and theoretical methods used for the study of nanocrystals reported in this thesis. In Chapter 3 of this thesis, we report results of theoretical studies carried out on III-V and II-VI semiconductors using the tight-binding (TB) methodology. Chapter 4 presents the investigations on the growth kinetics of several nanocrystal systems. Chapter 5 presents experimental investigations carried out on undoped and various transition metal (TM) doped ZnO nanocrystals. In summary, we have performed electronic structure calculations on various nanocrystal systems, devised a novel method to obtain the size distribution from UV-absorption spectrum and studied the mechanism of growth in the presence and absence of capping agents in various II-VI semiconductors. Using the optimal conditions obtained from the growth studies, we prepare high quality ZnO nanocrystals of required size, both in free-standing and capped states and doped it with small percentages of various transition metals like Mn, Cu and Fe. We have then studied their optical and magnetic properties.

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39

Wong, Ren-guei, and 翁仁貴. "Microstructure and Optical Properties of ZnO/CuInSe2 Semiconductor Compound Thin Film by Electrodeposition." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/57752940839078301140.

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碩士
吳鳳技術學院
光機電暨材料研究所
95
CuInSe2 is one of the most promising absorber materials for thin film solar cells. Furthermore, CuInSe2-based solar cells have shown long-term stability and the highest conversion efficiencies of all thin film solar cells, above 18 %. According to some reported papers, we believe it is a potential to combine electrodeposition CuInSe2 and ZnO for establishing a new route for CIS thin film solar cells development. In this study, two different electrodeposition methods (constant-potential and constant-current) have been applied to investigate the formation mechanism of the ZnO / CuInSe2 on indium tin oxide (ITO). The crystallinity , surface morphology, composition and transmittance of the co-deposition ZnO / CuInSe2 on ITO substrate were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe X-ray microanalyzer (EPMA), Energy Dispersive Spectrometer (EDS), and UV-Visible Spectrometer. Based on the experimental results, The dense ZnO films has been deposited onto n-type CuInSe2 from an aqueous solutions containing 1×10－3M ZnCl2 , 0.1 M KCl and 10×10－3 M H2O2 adjusted to pH=5. The as-deposited ZnO films had wurtzite structure with exhibited optical bandgap energy of 3.3 eV. XRD shows a preferential orientation (002) that increases strong depend on deposition time and pH value. Additionally, SEM micrographs show the ZnO electrodeposits consisted of columnar grains, which grew with c axis perpendicular to the substrate. Furthermore, Experimental results indicate that smaller grains, uniformity and higher transmittance of ZnO films from electrodeposition under constant-potential. At least we found that add complexing agent triethanolamine (TEA) will significant enhance ZnO / CuInSe2 adhesion.

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40

Huang, Tzu-yu, and 黃子祐. "The study of Physical Properties of Dilute Magnetic Semiconductor of Cobalt doped ZnO." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/60661651734823561458.

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碩士
國立中山大學
物理學系研究所
101
Doping of transition ions and introducing oxygen vacancies (VO) in several oxides can trigger spectacular room temperature ferromagnetic coupling and becomes diluted magnetic oxides. How the magnetic dopant and vacancies collaborate to induce ferromagnetism is still unclear. A general picture of the carrier mediated mechanism is widely accepted, such as: the free carriers mediate the long-range magnetic coupling via RKKY mechanism when the material is in metallic state while the localized carriers mediate magnetic coupling in a limited radius via BMP mechanism. For those semiconducting materials, the carrier is neither as free as metals nor localized as insulator, how electron induces magnetic coupling and who provides magnetic moments and what are the roles of doped transition ions and introduced oxygen vacancies are unclear and are needed to be answered before real applications. This study aims at developing a technique to reliably reproduce oxygen vacancies in Co doped ZnO films and growth a series samples with systematically varied oxygen vacancies to study these mentioned issues. In this study, five percent Co doped ZnO, Zn0.95Co0.05O (CZO), targets were prepared by solid state reaction method at 860oC. CZO films with various oxygen vacancies were grown by RF sputtering technique in a mixed H2/Ar gas with different percentages, denoted as H2%. It was found that the base vacuum of growth chamber is crucial for reliably reproduce exact vacancy concentration. With our effort, the base vacuum of our chamber is now lower than 1x10-7Torr and the VO reproducibility is reliable. These as grown films degraded very fast when were exposed to air. In order to know basic properties of the as grown films, the resistance and optical transmittance were measured right when films were taken out from the growth chamber. Films grown in high H2% atmosphere exhibit lower resistance, higher transmittance and wider optical bandgap which could be due to Burstein-Moss effect. The effective oxygen vacancies were measured by X-ray photon emission (XPS). Due to XPS is accessible in the core facility center which is usually few days or week after the film growth, only the data at the mid layer of films were taken. A slightly discrepancy between H2% and XPS data is found indicating a small uncontrollable in our film growth system. Reliable data has to be taken for only the as grown films. MCD data proves the doped Co ions substitutes successfully at Zn sites and shows magnetic coupling at around 3.4eV same as SQUID-VSM data indicated. These data strongly indicates that the doping of 5% Co alone cannot generate magnetic coupling, and only when coexist with oxygen vacancies the magnetic coupling appears.

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41

Wang, Wei-Chin, and 王偉欽. "Influence of hydrogen peroxide solution on properties of ZnO films and metal-semiconductor contact." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/yqxen3.

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碩士
國立成功大學
微電子工程研究所碩博士班
96
Besides having a wide direct bandgap of 3.37 eV, ZnO has an exciton binding energy of about 60 meV which is much higher than that of 22 meV and 25 meV for ZnSe and GaN, respectively. These benefits confirm the opto-electronic devices fabricated by ZnO material should have highly efficient performance at room temperature. Therefore the ZnO-based devices such as lighting-emitting diodes (LEDs), laser diodes (LDs), UV photodetectors, and solar cells have been recently proposed. In considering the ZnO-based LEDs, the fabrications of homo-structures still face much challenge. Owing to the non-stoichiometric property of making an undoped ZnO to be a n-type material, it is very difficult to obtain a highly doped p-type ZnO for the p-n junction. So we use MIS structure instead of p-n junction structure. Recently, nitrogen ion (N+) implantation and hydrogen peroxide (H2O2) solution were utilized to fabricate the ZnO-based MIS structures, On evaluating the production cost and simplifying the fabrication processes, the treatment by H2O2 solution is a better choice than the ion-implantation in obtaining an insulating ZnO layer. We immerse our sample in hydrogen peroxide to be an insulator layer. After that, Pt Schottky contact was deposited on peroxide-treated ZnO samples by thermal evaporation. Ti/Al contacts were used as an ohmic contact. We can get its I-V curve by HP4156.

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42

Yang, Ming-Da, and 楊明達. "High Frequency Magneto-transport Properties and Magnetism in Co-doped ZnO Dilute Magnetic Semiconductor." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/13164093234733240032.

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碩士
國立高雄師範大學
物理學系
94
Dilute magnetic semiconductors (DMS) have been extensively studied in recent years due to promising appliacation for spintronics. Oxide-diluted magnetic semiconductors (O-DMS) are particularly interesting to the coexistence of wide bandgap semiconducting and ferromagnetic properties. Many reports have elaborated on several experimental studies about room temperature ferromagnetism in Mn/Co/Ni-doped ZnO- and TiO2-based systems. Recent studies of the mechanism of ferromagnetism in Co:TiO2 have already come to the conclusion that the presence of free carriers is not required for this material to be ferromagnetic. Furthermore, the Co-doped TiO2 system was referred to as a “dilute magnetic dielectric” rather than DMS before. It is now an interesting research that we could extend Co-doped ZnO to other O-DMS systems which embrace the ferromagnetism and the dielectric state, and explore mechanism underlying for O-DMS. This thesis displays the study of high frequency impedance and dielectric properties of Zn1-xCoxO samples produced by solid-state reaction of mixing CoO with ZnO nano-powders. Moreover, the samples are annealed at 400-500℃ in 10-3torr vacuum. Structural and magnetic measurements of samples come out both before and after annealing. The crystalline structure quality is characterized by x-ray diffraction, Raman, HRTEM, EDXS, and Co-XAS spectra measurements. Also, there is no detectable evidence for the presence of Co metal or Co-rich clusters within the samples. The vibration sample measurement has shown the room temperature ferromagnetism of these samples under the circumstances of the vacuum annealing. The high frequency impedance spectra and dielectric properties, measured by impedance analyzer (HP4284), vary systematically with different doping of Co. Higher resistance and dielectrics of the samples are based on the vacuum annealing which enhances ferromagnetism. Our research provides the experimental evidence of the intrinsic ferromagnetism coexisting with the dielectric state in the Co:ZnO systems. The result suggests that the theoretical model of free charge carriers are not required for magnetic ordering in the O-DMS systems. Co-doped ZnO has the dilute magnetic dielectric behavior.

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43

劉子豪. "The Study of Optical and Electrical Properties of the Defect in ZnO Impurities Semiconductor." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/r6jmc3.

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碩士
大葉大學
電機工程學系
106
The purpose of this paper is investigating the zinc oxide films grown on quartz glass by using Rapid-Thermal Chemical Vapor Deposition(RTCVD) system.The ZnO films were grown at different heating temperatures(350 oC、400 oC、450 oC、500 oC)with 5hr.The ZnO samples were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),UV-Vis. The UV-Vis shows the average optical transmittance within the visible spectra is more than 70 %. From absorption peak to know energy gap respectively 3.26 eV、3.21 eV、3.23 eV and 3.24 eV.The SEM image shows the zinc oxide nanowires width is about 37.5 nm ~ 62.5 nm.

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44

Shao, Peng-Tsang, and 邵鵬蒼. "First-Principles Study of Optoelectronic Properties and Epitaxial Morphology of ZnO-based Semiconductor Alloy Films." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/37230910624210573673.

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碩士
國立中興大學
精密工程學系所
100
We conduct first-principles total-energy density functional of hybrid functional calculations to study the atomic structures, band structures, electronic structures,and epitaxial softening of Zn1-xMxO (M = Be, Mg, Cd, Ag, Cu) semiconductor alloys.We find the energy bandgap of Zn0.5Be0.5O and Zn0.5Mg0.5O increased to 4.1 eV and 3.58 eV, respectively. We also find the energy bandgap of Zn0.5Cd0.5O, Zn0.5Ag0.5O and Zn0.5Cu0.5O decreased to 1.52 eV, 0.95 eV and 1.18 eV, respectively.We find that the strong coupling between O 2p and Cu 3d or Ag 4d bands plays a key role in narrowing of band gaps and leading to the half-metallic behavior interpreted with the unique spatial distribution pattern between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO).We show that Zn1-xMxO systems will change the preferred orientation from ZnO to expect Zn0.5Cd0.5O.

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45

Chitara, Basant. "Properties And Applications Of Semiconductor And Layered Nanomaterials." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2288.

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This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc. Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2. The summary of the thesis is given at the end of the thesis.

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46

Chitara, Basant. "Properties And Applications Of Semiconductor And Layered Nanomaterials." Thesis, 2012. http://hdl.handle.net/2005/2288.

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This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc. Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2. The summary of the thesis is given at the end of the thesis.

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47

Liang, Yi-Hsiang, and 梁逸翔. "Optical properties of wide band gap semiconductors SiNx and ZnO." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/53362155734262519468.

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碩士
國立東華大學
材料科學與工程學系
94
Optical properties of the gap states in amorphous silicon nitride film deposited on GaAs (a-SiNx/GaAs) are characterized using piezoreflectance (PzR) and photoreflectance (PR) measurements at 15 and 300 K. The defect-state transitions of a-SiNx in both PR and PzR are temperature insensitive with respect to the direct band gaps of GaAs and silicon nitride. The temperature-insensitive behavior is an intrinsic character of an imperfection state existed in the middle gap of a semiconductor. Transition energies of all the gap-state transitions of a-SiNx/GaAs are analyzed by detailed line-shape fits to the PzR spectra. The origins of the gap-state transitions are properly assigned. Based on the experimental results together with previous density-of-states (DOS) calculations, an experimental band scheme including the transition assignments of the experimental gap states for a-SiNx/GaAs is constructed. Optical properties of the band-edge transitions of a ZnO film deposited on silicon substrate (ZnO/Si) are characterized using thermoreflectance (TR) measurements in the temperature range between 35 and 340 K. The TR spectrum of the zinc oxide film clearly shows a lot of transition features present at energies near 3.4 eV at 35 K. The observed TR features correspond to the A, B, and C excitonic series in the wurtzite ZnO. Transition energies of the A, B, C excitonic series are analyzed. The Rydberg constant and threshold energy for each A, B, and C excitonic series are determined. Temperature dependences of the transition energies of the A, B, and C series are analyzed. The parameters that describe the temperature variations of the excitonic transitions in the ZnO film are evaluated and discussed.

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48

Shih, Han-Yu, and 施函宇. "Studies and Applications of Optical Properties in Semiconductor Nanostructures: InGaN/GaN multiple quantum wells and ZnO nanorods." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/29910132514863910052.

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碩士
國立臺灣大學
物理研究所
96
Nanotechnology gives people a great future and conveniences. Semiconductor materials are widely made into nanostructures, and they show rather different electrical, magnetic, and optical properties from bulk materials. In this thesis, we investigated two semiconductor nanostructures, InGaN/GaN multiple quantum wells (MQWs) and ZnO nanorods, and found some novel phenomena. There usually exists a good piezoelectric effect in nitride wurtzite structure, such that InGaN/GaN MQWs have obvious build-in electric field in them, and this property could be used to construct a biosensor. As the hybridization process of deoxyribonucleic acid (DNA) occurs on InGaN/GaN MQWs, the electric field in MQWs would be altered by the polarity of DNA molecules, and the photoluminescence (PL) spectra, Raman spectra, and the calculated strain of InGaN lattice could also be changed due to the quantum confined Stark effect. As a result, InGaN/GaN MQWs have a great opportunity in the development of DNA-sequence identification. On the other hand, our group had found a phenomenon called photoelastic effect in ZnO nanorods last year, and we further expected that the thinner nanorods, the mightier photoelastic effect exists in them. In this thesis, three diameters of thick, mid-thick, and thin ZnO nanorods are studied. It was observed that the PL spectra, Raman spectra, and the calculated strain would be changed with different excitation Laser power. Besides, the amounts of change are greater in thinner nanorods. This result gives a good evidence to proof our expectation, and provides much novel information to optoelectric device developers.

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49

Shih, Han-Yu. "Studies and Applications of Optical Properties in Semiconductor Nanostructures: InGaN/GaN multiple quantum wells and ZnO nanorods." 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2207200814121700.

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50

Jung-ChuanLee and 李榮銓. "Investigations of structural, electrical, optical and magnetic properties of p- and n-type ZnO-based diluted magnetic semiconductor." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/37498744517839406742.

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